Effects of Orientational and Conformational Ordering on Isotactic Polypropylene Crystallization
Anderson D. S. Duraes, Wenlin Zhang
TL;DR
This study uses simulations to explore how different types of flow affect the crystallization of isotactic polypropylene, finding that conformational order is more important than orientational order for efficient nucleation.
Contribution
The paper introduces a novel approach combining flow-induced alignment and conformational ordering to understand polymer crystallization mechanisms.
Findings
Extensional flows cause stronger alignment in iPP compared to shear flows.
Conformational ordering significantly reduces the nucleation barrier in iPP crystallization.
Flow-induced orientational order alone does not promote rapid nucleation in simulations.
Abstract
We employ atomistic nonequilibrium molecular dynamics (NEMD) simulations to investigate the effects of homogeneous shear and uniaxial extensional flows on the crystallization of isotactic polypropylene (iPP) oligomers. Extensional flows induce stronger, molecular-weight-dependent alignment in iPP, whereas chains in shear flows exhibit weaker alignment that is independent of chain length. While both flow types promote uniaxial alignment of polymer segments, neither induces helical conformational order in iPP. Upon quenching below the melting temperature, flow-aligned chains tend to relax toward their isotropic state unless the flow stress is maintained, indicating that flow-induced orientational order alone is insufficient to promote rapid iPP nucleation in simulations. By inducing helical order in iPP chains via dihedral restraints, conformationally ordered chains quickly develop…
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Taxonomy
TopicsPolymer crystallization and properties · Material Dynamics and Properties · Rheology and Fluid Dynamics Studies